This invention concerns improvements in longitudinal compressive treatment of web materials and has particular application to microcreping and the softening of webs.
In U.S. Pat. No. 4,142,278, which is incorporated herein by reference, a two-roll longitudinal compressive treatment machine is shown in which one or two retarder blade elements are held in special relationship to the nip to impede the flow of the web for retarding and causing longitudinal compression of the web. The present invention provides improvements involving the rolls and the blades that enable the desirable characteristics of such two-roll machines and methods and other machines using web-drive rolls to be realized efficiently in commercial practice.
The invention also provides new approaches to designs of retarder blades that, in addition to being important in two-roll treatments, are more widely applicable, e.g. to single roll microcreping such as illustrated in U.S. Pat. Nos. 3,260,778 and 3,426,405, which are also incorporated herein by reference.
With machines and methods for longitudinal compressive treatment of web materials, there have been difficulties in achieving continuously reliable treatment, especially in the case of web materials that are highly heat-sensitive or have "stickiness" that makes them difficult to drive and process. There have also been problems related to general machine construction, blade stability and difficulty of maintaining proper process adjustment for the more difficult-to-treat materials. The present invention addresses these problems as well as providing general features useful in microcreping.